Oxidation of alcohols



Patented Nov. 7, 1933 l ,Charles Strosack er, Chester 0., Kennedy, and Earlv L. PeltomMidland, Mich., assignors to The Dow Chemical :Company -Midland, Mich., a v

, corporation of Michigan I No Drawing.

"Appljcatidn a ye'l; 1932 SeriatNo. 595,650

The present invention concerns an improved method of oxidizing alcohols, particularly monohydric aliphatic alcohols, with caustic alkali to produce aliphatic acids.

It has long been known that an aliphatic alco hol containing more than six'carbon atoms may be reacted with'solid sodium or potassium hydroxide at a temperature between about 240? and about 250 C. to form an alkali metal salt of the corresponding aliphatic acid in satisfactory yield, based on the quantity'of alcohol reacted, Guerbet, Bull; Soc. Chem; (4) 11, 164-9 (1912), for instance, reacted each of a series of aliphatic and substituted aliphatic alcohols (each; alcoholconing in thepresence of a large excess of caustic alkali from which the desired reaction product must subsequently be separated, so that the process is time consuming, costly to operate, and the yields are low when based on the quantity of caustic alkali employed. The method employed by Guerbet is still further disadvantageous, when applied to the production of acids from alcohols containing less than seven carbon atoms, in that, during the oxidation of said alcohols by the caustic alkali, considerable'quantities of the organic reactantsare converted toolefines and resinous by-products.

We have now found that a primary nion'ohydric aliphatic alcohol containing more than two carbon atoms may, in general, be reacted.

with a fused mixturerof sodium and potassium hydroxides, at a temperature between about 250 and about 300 C., to form an alkali metal salt of Y an aliphatic acid in comparatively good yield,

proved method, occurrence of the previously 're-i I ported undesirable side reactions, such as the formation of saturated hydrocarbons, olefines;

resinous by-products, carbonates, etc., is substantially prevented. We have found, still further, that by operating according tovv the, present method, the desired reaction maybe substantially completed in alrelatively short time ascompared with the time required when operating according to methods previously known. In addition to the I foregoingadvantages, we have found that by op;- erating according to our preferred method'here inafter described, the desired free aliphatic-acid product may be practically completely separated from'the reactionmixture in nearly pureform and as the substantially anhydrous compound.

To the accomplishment of the foregoing and related ends, the present inventiomthe'n, consists 76 of the method-hereinafter fully-described and particularlypointed out in the claims, the following description settingforth in detail several modesflof carryingout the invention, 'suchdis closedmodes illustrating, however, but several of the various ways in which the principle of our inventionmay be used' 7 i V A mixture of sodium and potassium hydroxides in respective quantities between the ratios of about] v I I 80 jINaOH- and about i V 'anaonf is heated to fusion in asuitable closed reactor pro; vided with a mechanical stirrer, an inlet'for alcohol, and an outlet for' gaseous products, The 0 fused alkaline mixture is stirred vigorously and thedesired quantity of a primary aliphatic alcohol is gradually contactedtherewith; the reaction mixturebeing maintained at'a temperature between about 250 and about 300 C. (preferably 9 between about 285 and about 295 C.) during the course of the reaction. The introduction of'alcohol to the reaction mixture is continued, preferably, until-from about 85 to'about per cent of the caustic alkali initially employed is reacted.

Under optimum operating conditions substan- 1 tially all of the alcohol employed may be reacted directly-with the-fused alkali metal hydroxide, but ordinarily a portion of the alcohol admitted to the reactor passes through the same unreacted. The unreacted alcohol may be condensed from its admixture with hydrogen, which is generated; during the reaction, and returned to the'rea'ctor.

After the desired quantity of alcohol is reacted,

we have found-that the reaction mixture may, in 11g 7 I hydroxide employed;

to substantially neutralize the mixture.

formed. In order to avoid such contaminationv and at the same time obtain the product in anhydrous form, we have found that the heated and stirred reaction mixture may advantageously be treated with an aqueous solution of an aliphatic acid (corresponding to that formed through oxidation of the alcohol used) in quantity sufficient During the course of such neutralization, the water added is vaporized, and efiectively. steam distills all unreacted alcohol from the mixture. Heating of the fused mixture is continued until practically, all water is vaporized therefrom. Themixtureis then cooled to solidification, pulverized, acidified with a strong-mineral acid,.such as gaseous hydrogen chloride'or. concentrated sulphuric acid (preferably the latter), and the aliphatic acid is distilled from the ac'idifiedmixture. When sulphuric acid is employed to acidify the neutralized reaction mixture, the latter should be cooled to a temperature sufficiently lowso that components salts of the same,-in that by means of such method practically all of the aliphaticacidin the reaction mixture may be separated directly, in nearly pure form, and as the substantially anhydrous compound. The aliphatic acid product may, however, be separated from the previously described reaction mass in any of the usual ways, e. gQby'direct acidification of the cooled alkaline reaction mixture with a strong mineral acid and distillation ofthe aliphatic acid productfrom thev acidified mass. The latter method isdisadvantageous over our preferred method in that the aliphatic acid thereby separated generally contains an appreciable quantity of water which, frequently, may be removed from the product only with extreme difficulty.

Through operating according to our'preferred procedure, a primary monohydric aliphatic alcohol may be oxidized to form an alkali metal salt of the corresponding aliphatic acidin relatively high yield, based on both the quantity of alcohol reacted and on the quantity of alkali metal undesirable side reactions, such as the formationof saturated hydrocarbons, olefines, carbonates, etc., are practically avoided and a substantially anhydrous aliphatic excellent yield and as the practically pure compound.

When normal propyl alcohol is reacted with a fused mixture of sodium and potassium hydroxides according to our improved method, propionic acid may be recovered from the reacted mass through procedure similar to that previously described. If desired, however, the reacted mixture may be dissolved in aqueous sodium hydroxide and sodium propionate be crystallized from the resultant solution. The mother liquor may be evaporated to dryness, and the residue, which will consist ofpotassium hydroxide and residual sodium hydroxide and alkali metal propionate,' may be returned to the initial reaction wherein it maybe employed for the oxidation of additional quantities of alcohol.

' As previously stated, any primary monohydric aliphatic alcohol containing more than 2 carbon atoms may be oxidized according to the method herein described and an alkali metal salt of the corresponding aliphatic acid. be formed in excellent yield. In the case of ethyl alcohol, however, a considerable portion of the alcohol is decomposed to form ethylene,,so that for the successful oxidation of ethyl alcohol with fused caustic alkali, special precautions are required, which are particularly described and claimed in our copending application Serial No. 593,086, filed February 15, 1932.

In the accompanying table of examples are described the results obtained when various monohydric. aliphatic alcohols were oxidized according to our improved method. In each of the runs described, a substantially. anhydrous .miX- ture of sodium and potassium hydroxides in the respective quantities shown was placed in an enclosed iron reactor provided with a mechanical stirrer, an inlet foralcohol andan outlet for gaseous products, 13. g, hydrogen. The alkali metal hydroxide mixture was heated to fusion and maintained at the temperature indicated, with stirring, while the desired alcohol was gradually contacted therewith. During the course of the reaction hydrogen, which was evolved from the stirred mixture, was conducted from the reactor through a condenser wherein any alcohol which had passed through the reactor unreacted was condensed as a liquid. The unreacted alcohol was weighed and-the difference between the quantity of alcohol employed and the quantity recovered as unreacted material was the quantity of alcohol reacted. The quantities of alcohol shown in the table are the quantities calculated as havingbeen reacted.

After the reaction was substantially completed, the reaction mixture was cooled, dissolved in water and the respective quantities of alkali metal acid is separated from the reaction mixture in hydroxide, carbonate, and aliphatic acid prod- I Table of examples Alcohol Caustic alkali Products-Moles Yields of g z Percent Reaction of alkali it? 0% Alkali W 3" d ff ff FOX! Base on a ill on a mi Kind Moles gn i MES-Egg metal-11y Acid consumed on alcohol metal hymetal hyreacted Moles KOH droxide t d d d He played ted reac e roxi e IOXl mesa charged consumed 1 9. 43 10 v 1/1 290 0. 676 8. 77 93. 2 93. 0 87. 7 94. l 2 7. 64 10 l/l 290 2. 16 7. 41 78. 4 97. 0 74. l 94. 6 3 9.3 10 1/1 290 0. 63 9. 19 93. 7 98. 8 91. 9 98. 2 4 12. 8 i 15 2/1 285-295 1. 71 12. 04 88. 6 94. 1 80. 3 90. 7 5 2. 185 3 1/1 290 0. 673 2. 065 77. 6 94. 68. 8 88. 7

ii'cts present were determined-through analysis.

of aliquot portions of the resultant solutionrl it In the examples,it will be noted that the desired aliphatic acid was in each instance formed in a yield of 93 per cent of theoretical orhigher, based on the quantity of alcohol reacted. In runs 1, 3, and 4 more than 88 per cent of the alkali metal hydroxide employed was reacted to form the desired alkali metal salt of the aliphatic acid. In'runs' l, 3, and 4 the alkali metal salt offth'e aliphatic acid was'formed in a yield-greater than 80 per cent of theoretical, based on the quantity of alkali metal hydroxide'employed; and greater than 90 per cent of theoretical based on the quantity of alkali metal hydroxide reacted. 'Runs 2 and 5 were made for the purpose of determining the possible yield of acid based on thequantity of alcohol reacted. In each of the last mentioned runs, the reaction was still progressing rapidly when the addition of.-a1coh0l was discontinued.

The principle of our invention may be practiced in ways other than those previously described; The higher primary monohydric aliphatic alcohols, such as n-octyl" alcohol, n-nonyl alcohol,,, cetyl alcohol, etc., may for instance .be reacted,

with a fused mixture of :sodium and potassium hydroxides, according to our improved method, and the corresponding aliphatic acids be obtained in excellent yield.

We have previously stated that a fused caustic alkali mixture initially containing sodium; and

potassium hydroxides in, a molecular ratio between about r lNa OH ZKOH and about 'SNaOH lKOI-I may be employed as an agent for the oxidation of alcohols according to our method. When certain alcohols, e. g. some of the higher aliphatic alcohols, are to be oxidized according .to the present method and mixtures of sodium, and potassium hydroxides initially containing sodium hydroxide in a proportion appreciably greater than thatrepresented by the molecular ratio lNaOH IKOH are employedfas oxidizing agents, the reaction mixturemay tend to become thick and 'diflicultto stir as the reaction proceeds,- and, indeed may sometimes even solidify. If a reaction mixture becomes difficult to stir, it may be made more liquid by adding eitherthe alkali metal hydroxide or the alkali metal salt ofthe aliphatic acid product required to shift the ratio of sodium and potassium compounds in the reaction mixture toward an equimolecular basis. 'We frequently find it advantageous, however, to avoid difliculties such as those last described, by employing a fused caustic alkali'mixture which initially contains sodium and potassium hydroxides .in respective amounts betweenthe molecular ratios of about INaOI'lI IKOH and about lNaOH 2KOH Although anyu'eaction temperature between about 250and about 3Q0 C. may be employed in practicing our invention, we prefer to maintain the reaction 'mixture at a temperature between mately atmospheric pressure.

: of such stated step or steps be employed.

about 285 and about2 C. When the reaction temperature is maintained below about 285 C. the

reaction may become sluggish so that the time requantity (2 to 8 per cent) of water, or if the fused alkaline "mixture is substantially saturated with water under the reaction conditions maintained, the reaction temperature may be raised to about 325 C. without material decomposition or over oxidation of the product occurring. Apparently water tends to prevent undesirable side reactions but at the'sametime tends to slow up the principal reaction. The presence of a relatively small "quantity of water in the reaction mixture, therefore, may at times be highly desirable, although the presence of'any considerable quantity (e. g. more than about 15 per cent in the fused alkaline mixture or more than about 8 per cent in the alcohol) should be avoided.

It is important to stir the fused reaction mix- I ture vigorously during the addition of the alcohol, so as to expose unreacted hydroxide continually to contact with the alcohol. While the reaction will occur under the operating conditions previously described, even though the mixture is not stirred, stirring maintains the mixture in a substantially homogeneous condition, prevents local overheating of the fused mixture and resultant decomposition of the desired product, and, in general, aids in obtaining smooth reaction between the alcohol and the alkali. I

The results shown in the table were obtained when the alcohols were reacted with the fused alkali metal hydroxide mixture under approxi- The reaction may insome instances, howevenbe carried out advantageously under increased pressure; particularly when the reactants contain an appreciable quantity of water. If an alcohol containing about 5 per cent of water is to be oxidized, for instance,

an increase in pressure aids in maintaining suitable contact between all reactants and not only shortens the time required for reaction at a given temperature, but also aids in effecting substantially complete reaction. Generally, the pressurene'ed not exceed about 4 atmospheres to assure smooth reaction. a

Other modes of employing the principle of our invention may be employed instead of those ex- ,plained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent We therefore particularly point out and disf tinctly claim as our invention:

1. In a method of'making an aliphatic acid, the

f step which consists in reacting a primary monohydric aliphatic alcohol, containing more than ,two carbon atoms, with a fused mixture initially containing sodium and potassium hydroxides i a, molecular ratio between about lNaOH ZKOH- CIl and about t'ass'ium hydroxides in a molecular ratio between about 1 I lKOI-I M 1 2KOI-I the fused mixture being maintained at a temperaand about ture between about 250 and about 325 C. during 3NaOH the course of the. reaction. fi"

2. In a method of making an aliphatic acid, the steps which consist in reacting a primary monohydric aliphatic alcohol, containing more than two carbon atoms with a fused mixture initially containing-sodium and potassium hydroxides .in a molecular ratio between about lNaOI-I ZKOH and about lNaOH lKOI-I stirring the fused mixture and maintaining the same at a temperature between about 250 and about 300 C. during the course of the reaction.

3. In a method of making an aliphatic acid, the steps which consist inintroducing a primary monohydric aliphatic alcohol, containing more than two carbon atoms, into contact with a fused mixture which initially contains sodium and potassium hydroxides in a molecular ratio between about lNaOI-I ZKOH and about 1N aOH lKOI-I stirring the fused reaction mixture and maintaining the same at a temperature between about 250 and about 300C. during the course of the reaction, acidifying the reacted mixture with a strong mineral acid .to liberate the free aliphatic acid product, and separating the latter from the acidified mass. p

i. In a method of making an aliphatic acid, the steps which consist in introducing a primary monohydric aliphatic alcohol; containing more than two carbon atomainto contact with a fused mixture which initially contains sodium and potegssiiun hydroxides in a molecular ratio between a ou lNaOI-I 2 KOH and about mixture to remove moisture therefrom, cooling to solidification, acidifying with a concentrated strong m neral acid, and. distilling the aliphatic acid product from the acidified mass.

'5. In a method of making an aliphatic acid, the.

steps which consist in reacting a primary monohydric aliphatic alcohol, containing more than two and less than seven carbon atoms, with a fused mixture initially containing sodium and postirring the reaction mixture and maintaining the same at a temperature between about 250 and about 325 C. during the course of the reaction.

6. In a. method of making an alkali metal salt of an aliphatic acid, the steps which consist in reacting a primary monohydric aliphatic alcohol, containing more than two and less than seven carbon atoms, with a fused mixture initially containing sodium and potassium hydroxides in a molecular ratio betweenabout I 1Na0H 2KOI-I and about SNaOH stirring the fused reaction mixture andmaintaining the same at a temperature between about 250 and about 300 C. during the course of the reaction, acidifying the reacted mixture with a strong 'mineral acid to liberate the free aliphatic acid product, and separating the'latter from the acidified mass, Y

8. In a method of making an aliphatic acid, the steps which consist in introducing a primary monohydric aliphatic alcohol, containing more than'two and less than seven carbon atoms, into contact with a fused mixture which initially contains sodium and potassium hydroxides in a molecular ratio between about lNaOH 2KOH and about u ixon therefrom, cooling the mixture to solidification,

acidifying with a concentrated strong mineral acid anddistilling the aliphatic acid product from the acidified mass. i

- 9. In a method of making an aliphatic acid, thesteps which consist in introducing a primary monohydric aliphatic alcohol, containing more than two and lessthan seven carbon atoms, into' contact with a fused mixture which initially contains sodium and potassium hydroxides in a molecular ratio between about 1NaOH Q and about v .SNaOI-I 1x011 stirring the fused reaction mixture and maintaining the same at a temperature between about 250 andabout 300 ,Ciduring the course of the reaction; condensing unreacted alcohol which is evolvedduring the reaction and re-" the steps which consist in introducing a primary I monohydric aliphatic alcohol, containing more thantwo and less than seven carbonatorns, into contact with a fused mixture which initially con- 1 tains sodium and potassium hydroxides in a molecular ratio 7 between about 1; maon. r T. K

and about stirring the fused reaction mixture and main-' taining the same at a temperature between about 250 and about 300 C. during the course of the reaction, condensing unreacted alcohol which is evolved during the reaction and returning the condensed alcohol to the reaction, substantially neutralizing the reacted mixture with an aqueous solution of the aliphatic acid corresponding to that formed through oxidation 3 of the alcohol employed, heating the neutralized mixture to remove substantially all water and other volatile components therefrom, cooling to a temperature such that components thereof will not be appreciably oxidized by concentrated sulphuric acid, acidifying the mixture with concentrated sulphuric acid and distilling the aliphatic acid product from the acidified mass.

11. In a method of making analiphatic acid, the steps which consist in neutralizing a fused alkaline mixture containing an alkali metal salt of said acid with an aqueous solution of the free aliphatic acid, heating the neutralized mixture to remove water and other volatile components therefrom, cooling to solidification, acidifying with a concentrated strong mineral acid and distilling the aliphatic acid product from the acidi- 12. In a method of making propionic acid the step which consists in. reacting normal propyl alcohol with a fused mixture initially containing sodium and potassium hydroxides'in a molecular. ratio between about ratio between about and about:

the fused mixture beinginaintained at a term perature between about 250 and about 325 C. duringthe course of the reaction.

7 13. In a method of making propionic acid, the steps which consist in reacting normal propyl alcohol with a fused mixture-initially containing sodium and potassium hydroxides in a molecular stirring the fused ,niixture and maintaining the same at atemperature between about 25c? and about 300C, during the courseof the reaction.

14. In a method of making piopionic acid, the

steps which consist in introducing normal propyl alcohol into contact with a fused. mixture which initially contains sodium and potassium hydroxides in a molecular ratio between about I and about among lKOI-I stir-ring the fused reaction mixture and maintaining the same at-atemperaturebetween about 250 and about 300 C. during the course of the reaction, substantially neutralizing the reacted mixture with propionic acid, heating the neutralized mixture to remove substantially all moisture therefrom, cooling the mixture to solidification, acidifying with a strong mineral acid and distilling propionic acid from the acidified mass.

15. In a method of making butyric acid, the

step which consists in reacting normal butyl alcohol with a fused mixture initially containing sodium and potassium hydroxides in a molecular ratio between about lNaOI-I ZKOH and about the fused mixture being maintained at a temperature between about 250 and about 325 C.

during the course of the reaction.

16. Ina method of making butyric acid, the steps which consist in reacting normal butyl alcohol with a fused mixture initially containing 3' sodium and potassium hydroxides in a molecular ratio between about lNaOH ZKOH and

stirring the fused mixture and maintaining the same at a temperature between about 250 and about 300 C. during the course of the reaction.

17. In a method ofmaking butyric acid, the steps which consist in introducing normal butyl alcohol into contact with a fused mixture which initially contains sodium and potassium hydroxides in a molecular ratio between about and about lNaOH 2KOH and about SNaOI-I' lxor-r the fused mixture being maintained at a temperature between about 250. and-about 325 C. during the course of the reaction.-

19. In a method of making isovaleric acid, the steps which consist in reacting iso-amyl alcohol with a fused mixtureinitialiy containing sodium and potassium hydroxides in -a molecular ratio between about r lNaOI-I ZKOH and

INaOI-I" lKOH stirring the fused mixture and maintaining the same at a temperaturebetween about 250 and about 300 C. during the course of the reaction.

20. In a method of making isovaleric acid, the steps which consist in introducing iso-amyl alcohol into contact with a fused mixture which initially contains sodium and potassium hydroxides in, a molecular ratio between about 1N aOH ZKOH and about stirring the fused reaction mixture and maintaining the same at a temperature between about 250 and about 300 C. during the course of the reaction, substantially neutralizing the reacted mixture with isovaleric acid, heating-the neutralized mixture to remove substantially'all moisturetherefrom, cooling the mixture to solidificatiomvacidifying with a strong mineralcacid and distilling isovaleric acid from the acidified mass. i

CHARLES J. STROSACKER. CHESTER C. KENNEDY. EARL- L. PELTON. 

